The invention relates generally to electrical machines. More particularly, the invention relates to a laminated rotor assembly for an electrical machine.
A typical design approach for a laminated rotor assembly includes shrink fitting a stack of laminations onto a shaft. The resulting shrink fit is used to transmit toque from the shaft to the laminations. Only the shaft provides stiffness and support for the laminations. Due to material limitations and shaft stiffness requirements, however, this approach results in a rotor assembly having a low tip speed, low relative stiffness and, consequently, poor dynamic performance.
Dynamic performance can be improved by increasing the stiffness of the lamination stack. Increasing the stiffness decreases the amount of deflection during operation at high rotational speeds and/or high operating temperatures.
Stiffness can be increased by clamping the lamination stack with a central tieshaft. Higher clamping loads result in higher stiffness. However, the higher clamping loads also decrease efficiency of the electrical machine. Magnetic insulation layers are not well maintained under high clamping loads, and core losses are increased. Moreover, the tieshaft interferes with the cooling of the lamination stack.